Tutorial by Examples: define

class Message DEFAULT_MESSAGE = "Hello, world" def speak(message = nil) if message puts message else puts DEFAULT_MESSAGE end end end The constant DEFAULT_MESSAGE can be changed with the following code: Message::DEFAULT_MESSAGE = "Hullo, wo...

There are a number of predefined global variables that you can set in the front matter of a page or post. VariableDescriptionlayoutIf set, this specifies the layout file to use. Use the layout file name without the file extension. Layout files must be placed in the _layouts directory.permalinkIf y...

This linker error happens, if the linker can't find a used symbol. Most of the time, this happens if a used library is not linked against. qmake: LIBS += nameOfLib cmake: TARGET_LINK_LIBRARIES(target nameOfLib) g++ call: g++ -o main main.cpp -Llibrary/dir -lnameOfLib One might also for...

module.exports.routes = { // This function will be executed for all http verbs on all urls 'all /*', function (req, res, next) { // Expose the function `fooBar` to all views (via the locals object) res.locals.fooBar = function (arg1) { return 'foobar' + arg1; }; }, };...

User-defined functionals Users can create their own functionals to varying degrees of complexity. The following examples are from Functionals by Hadley Wickham: randomise <- function(f) f(runif(1e3)) lapply2 <- function(x, f, ...) { out <- vector("list", length(x...

It is easy to get confused in the C preprocessor, and treat it as part of C itself, but that is a mistake because the preprocessor is just a text substitution mechanism. For example, if you write /* WRONG */ #define MAX 100; int arr[MAX]; the code expands to int arr[100;]; which is a synta...

For some use cases, you can use the using syntax to help define a custom scope. For example, you can define the following class to execute code in a specific culture. public class CultureContext : IDisposable { private readonly CultureInfo originalCulture; public CultureContext(string ...

The most important consequence of the One Definition Rule is that non-inline functions with external linkage should only be defined once in a program, although they can be declared multiple times. Therefore, such functions should not be defined in headers, since a header can be included multiple tim...

In order to be able to use a class as the key in a map, all that is required of the key is that it be copiable and assignable. The ordering within the map is defined by the third argument to the template (and the argument to the constructor, if used). This defaults to std::less<KeyType>, w...

Typed holes can make it easier to define functions, through an interactive process. Say you want to define a class instance Foo Bar (for your custom Bar type, in order to use it with some polymorphic library function that requires a Foo instance). You would now traditionally look up the documentati...

Sometimes it may be useful to have a specific asBoolean definition in your own program for some kind of objects. /** an oversimplified robot controller */ class RunController { def complexCondition int position = 0 def asBoolean() { return complexCondition(this...

You can define the signing configuration in an external file as a signing.properties in the root directory of your project. For example you can define these keys (you can use your favorite names): STORE_FILE=myStoreFileLocation STORE_PASSWORD=myStorePassword KEY_ALIAS=myKeyAlias KEY_PASSWOR...

You can store the signing information setting environment variables. These values can be accessed with System.getenv("<VAR-NAME>") In your build.gradle you can define: signingConfigs { release { storeFile file(System.getenv("KEYSTORE")) storePasswo...

A common use of macros is to create templates for data structures which obey common rules but may contain different fields. By writing a macro, you can allow the detailed configuration of the data structure to be specified without needing to repeat boilerplate code, nor to use a less efficient struc...

It took me a while to get this right, so I decided to share a solution because it might save someone else several days of trial and error. The problem: I want to be able to enable/disable WCF tracing in my C# .NET application and choose the trace output filename. I don't want users editing the .con...

get_defined_vars() returns an array with all the names and values of the variables defined in the scope in which the function is called. If you want to print data you can use standard functions for outputting human-readable data, like print_r or var_dump. var_dump(get_defined_vars()); Note: This...

In Julia, as in many other languages, it is possible to interpolate by inserting values defined by variables into strings. For a simple example: n = 2 julia> MyString = "there are $n ducks" "there are 2 ducks" We can use other types than numeric, e.g. Result = false j...

An internally defined exception doesn't have a name, but it has its own code. When to use it? If you know that your database operation might raise specific exceptions those which don't have names, then you can give them names so that you can write exception handlers specifically for them. Otherwis...

Predefined exceptions are internally defined exceptions but they have names. Oracle database raise this type of exceptions automatically. Example create or replace procedure insert_emp is begin insert into emp (emp_id, ename) values ('1','Jon'); exception when dup_val_on_index then ...

As the name suggest user defined exceptions are created by users. If you want to create your own exception you have to: Declare the exception Raise it from your program Create suitable exception handler to catch him. Example I want to update all salaries of workers. But if there are no work...